The document provides an overview of the geologic time scale, highlighting the divisions and significant life forms present across various periods, from the early formation of Earth 4.6 billion years ago to contemporary life. It discusses the principles of relative and radiometric dating, guide fossils, and notable extinct and evolving species, illustrating changes in Earth's environment and biodiversity over time. Key scientific contributions to geologic principles and the study of fossils are also detailed, emphasizing their role in understanding Earth's history and the evolution of life.

1. After going through this lesson, you should be able to:
1. Identify and describe the subdivisions of the geologic time
scale and the life forms present in different periods;
2.Describe and recognize the importance of guide fossil in
identifying subdivisions of the geologic time scale;
3.Identify significant events happened throughout earth’s
history;

4. GEOLOGIC
TIME
SCALE

5. GEOLOGIC TIME SCALE
-serves as the calendar for events in Earth’s
history
-serves as standard timeline used to describe
the age of rocks, fossils and the events that
formed them

6. GEOLOGIC TIME SCALE
RELATIVE DATING- first basis of and for geologic
time scale
RADIOMETRIC DATING- numerical dates of rocks
were determined
INDEX FOSSILS- use of marker fossils leading to
determination of organisms predominantly living
at a certain time and age.

24. GEOLOGIC TIME SCALE
MYA ERA PERIOD EPOCH PLATE TECTONICS LIFE
0.01
Cenozoic
“Age of
Mammals”
Quaternary
Holocene Beaches and barrier islands form
-Mastadons become extinct
-Human culture flourishes
-Accelerating extinction of many
species
1.8 Pleistocene Ice sheets form
-Modern humans develop
-Asians arrive and settle the
Americas
5.3
Tertiary
Pliocene
-Volcanic activity in North
America and Africa
-Grand Canyon forms
Hominids develop
23.8 Miocene Sandhills form in S.C.
Horses, mastadons, mammoths,
tigers, and camels live in South
Carolina
33.7 Oligocene
Appalachians uplift; erosion
increases
Cats, dogs, and apes appear
54.8 Eocene
Sea levels rise; deposits of marine
sediments – limestone in S.C.;
land bridges form
-Grass spreads widely
-Diverse array of animals develop,
including whales, rhinos, and
elephants
65.0 Paleocene
Earthquakes common; Georgia
Embayment, Cape Fear Arch
forms in Southeast
-First horses appear (size of a cat)
-Tropical plants dominate
144
Mesozoic
“Age of
Reptiles”
Cretaceous
Mass extinction occurs at the end
of the period caused by a
meteorite impact (Dinosaurs,
ammonites and 25% of marine life
become extinct)
-T-Rex develops but number of
dinosaur species decline
-Snakes appear and first primates
appear
-Angiosperms appear
206 Jurassic
Western US: orogeny of Rockies;
North America continues to rotate
away from Africa
-First birds appear
-Golden age of dinosaurs
248 Triassic
-Pangea begins to break apart
-Rocky Mountains and Sierra
Nevada form
First dinosaurs, mammals,
crinoids, and modern echinoids
appear
290 Permian
-Pangea forms
-Appalachians rise
-90% of Earth’s species become
extinct, including trilobites,
blastoids, fish and amphibians
because of heavy volcanism in
Siberia 24
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25. 320
Carboniferous
Pennsylvanian
Great swamps develop (future
coal deposits
-Reptiles develop from
amphibians
-Flying insects appear
354 Mississippian
Much of North America is under
water
-First seed plants appear
-Sea life flourishes including
coral, brachiopods, blastoids, and
bryozoa
417 Devonian
Acadian Orogeny – SC
metamorphism
-Dominant animals: fish
-Amphibians, evergreens and
ferns appear
443 Silurian Extensive erosion
First land plants appear and land
animals follow
490 Ordovician
-Beginning of the construction of
South Carolina
-Great extinction due to growth of
ice caps including in what is now
northern Africa
-First animals with bones appear
-Dominant animals: marine
invertebrates including corals and
trilobites
540 Cambrian
S.C. near the equator; island arc
continues to move toward North
America
-Explosion of life
-All existing phyla came into
being here
-Life forms in warm seas as
oxygen levels rose enough to
support life
-Dominant animals: trilobites and
brachiopods
4600
Precambrian
(Hadean, Archean, and Proterozoic Ages)
Earth takes 10 million years to
cool: initial atmosphere escapes
into space (H&He) and the core
forms (Fe&Ni)
Volcanic outgassing of water and
carbon dioxide occurred for
millions of years, helping to build
atmosphere and then oceans
At 3 billion years ago, banded
iron formation rocks appear due
to rising oxygen levels in the
atmosphere and sea
No life possible as the Earth
initially forms 4.6 billion years
ago.
Simple, single-celled forms of life
appear 3.8 billion years ago.
They will become more complex
and successful over the next 3
billion years: Prokaryotes then
Eukaryotes
Cyanobacteria begins producing
free oxygen (photosynthesis)
Paleozoic
“Age of
Invertebrates”
Modified after Carolina Rocks, contributed by J. Westmoreland 7
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26. Principles Behind Geologic Time
 Nicholas Steno, a Danish physician (1638-1687), described how the position of a rock layer could
be used to show the relative age of the layer. He devised the three main principles that underlie the
interpretation of geologic time:
 The principle of superposition: The layer on the bottom was deposited first and so is the oldest
 The principle of horizontality: All rock layers were originally deposited horizontally.
 The principle of original lateral continuity: Originally deposited layers of rock extend laterally
in all directions until either thinning out or being cut off by a different rock layer.
 These important principles have formed the framework for the geologic area of stratigraphy,
which is the study of layered rock (strata).
 Decades later, other European scientists rediscovered ‘Steno’s Laws’ and began applying them.
Abraham Gottlob Werner became famous for his proposal that all rocks came from the ocean
environment. He and his followers were called “Neptunists.” An opposing view (by Voisins)
argued that all rocks of the earth came from volcanic environments. These scientist were called
“plutonists.”
Older
Younger
Geologist studying the stratigraphy in
the Copper Basin, Idaho. These rock
layers were deposited horizontally,
and uplifted later so they are now
tilted at an angle (along the red arrow).
(Photo contributed by K. McCarney-Castle)
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27.  James Hutton, a Scottish physician and geologist (1726-1797), thought the surface of the earth
was an ever-changing environment and “the past history of our globe must be explained by what
can be seen to be happening now.” This theory was called “uniformitarianism,” which was later
catch-phrased as “the present is the key to the past.”
 William Smith was a surveyor who was in charge of mapping a large part of England. He was
the first to understand that certain rock units could be identified by the particular assemblages of
fossils they contained. Using this information, he was able to correlate strata with the same fossils
for many miles, giving rise to the principle of biologic succession.
 The principle of biologic succession: Each age in the earth’s history is unique such that
fossil remains will be unique. This permits vertical and horizontal correlation of the rock
layers based on fossil species.
Even though these two outcrops are
separated by a large distance, the same
rock layer can be correlated with the
other because of the presence of the
same shark teeth. This lets scientists
know that the two layer were deposited
at the same time, even if the surrounding
rocks look dissimilar from each other.
300 km
Rock Outcrop 1
Rock Outcrop 2
Principles Behind Geologic Time, continued
9
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28.  During the early 1800’s, English Geologist, Charles Lyell published a book called “Principles of
Geology,” which became a very important volume in Great Britain. It included all of Hutton’s
ideas, and presented his own contemporary ideas such as:
 The principle of cross-cutting relationships: A rock feature that cuts across another feature
must be younger than the rock that it cuts.
 Inclusion principle: Small fragments of one type of rock but embedded in a second type of
rock must have formed first, and were included when the second rock was forming.
 The theory of natural selection was credited to Darwin (along with Alfred Russel Wallace) and
he went on to write the famous “Origin of Species.” Darwin’s two goals in that work were:
1. To convince the world that evolution had occurred and organisms had changed over
geologic time
2. The mechanism for this evolution was natural selection.
 Charles Darwin (1809-1882) was an unpaid naturalist who signed up for a 5-yr
expedition around the world aboard the H.M.S. Beagle. On this trip, he realized
two major points. In spite of all species reproducing, no one species overwhelmed
the Earth, concluding that not all individuals produced in a generation survive. He
also found that individuals of the same kind differ from one another and concluded
that those with the most favorable variations would have the best chance of
surviving to create the next generation.
Principles Behind Geologic Time, continued
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29. The Earth Through Time
Standard 8-2.5: Illustrate the vast diversity of life that has been present on Earth over time by using the geologic time scale.
 No life possible as the Earth initially forms 4.6
billion years ago.
 Simple, single-celled forms of life appear 3.8
billion years ago, becoming more complex and
successful over the next 3 billion years:
Prokaryotes then Eukaryotes
 Cyanobacteria begins producing free oxygen
(photosynthesis)
 Land masses gather to make up a continent
called “Rodinia”
Cambrian:
 Explosion of life
 All existing phyla come into being at this time
 Life forms in warm seas as oxygen levels rise
enough to support life
 Dominant animals: Marine invertebrates
(trilobites and brachiopods)
 Supercontinent Gondwana forms near the South
Pole (note position of present-day Florida)
The Proterozoic:
PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002 29
19
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30. Ordovician:
Silurian:
 The 1st animals with bones appear, though
dominant animals are still trilobites, brachiopods
and corals
 The beginning of the construction of South
Carolina
 A very cold time in Earth’s history: there was a
great extinction due to ice caps in present-day
Africa
 Four main continents: Gondwana, Baltica,
Siberia and Laurentia
 First land plants appear and land animals follow
 Laurentia collides with Baltica and closes
Iapetus Sea.
 Coral reefs expand and land plants begin to
colonize barren land.
 First millipede fossils and sea scorpions
(Euryptides) found in this period
PaleoMaps used with permission from Christopher
Scotese and are under copyright of C.R. Scotese, 2002
30
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31. Devonian (Age of the Fish)
Mississippian:
 First seed plants appear
 Much of North America is
covered by shallow seas and sea
life flourishes (bryoza, brachipods,
blastoids)
Pennsylvanian:
 Modern North America begins
to form
 Ice covers the southern
hemisphere and coal swamps
formed along equator.
 Lizards and winged insects first
appear.
 Pre-Pangea forms. Dominant animal:
fish
 Oceans still freshwater and fish
migrate from southern hemisphere to
North America.
 Present-day Arctic Canada was at the
equator and hardwoods began to grow.
 Amphibians, evergreens and ferns
appear
 The Acadian Orogeny, leading to S.C.
metamorphism
PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002
31
21
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32. Permian:
 Last period of the Paleozoic
 Pangea forms. Reptiles spread
across continents.
 The Appalachians rise
 90% of Earth’s species become
extinct due to volcanism in Siberia.
This marks the end of trilobites,
ammonoids, blastoids, and most
fish.
Triassic:
 First dinosaurs appear
 First mammals- small rodents appear
 Life and fauna re-diversify
 Rocky Mountains form.
 First turtle fossil from this period
 Pangea breaks apart
PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002
22
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33. Jurassic:
 Pangea still breaking apart
 Dinosaurs flourish “Golden age of
dinosaurs”
 First birds appear
 North America continues to rotate away
from Africa
Cretaceous:
 T-Rex develops
 First snakes and primates appear
 Deciduous trees and grasses
common
 First flowering plants
 Mass extinction marks the end of
the Mesozoic Era, with the demise
of dinoaurs and 25% of all marine
life.
PaleoMaps used with permission from Christopher Scotese and are under copyright of
C.R. Scotese, 2002
33
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34. Tertiary:
 First horses appear and tropical
plants dominate (Paleocene)
 Grasses spread and whales, rhinos,
elephants and other large mammals
develop. Sea level rises and
limestone deposits form in S.C.
(Eocene)
 Dogs, cats, and apes appear
(Oligocene)
 Horses, mastadons, camels, and
tigers roam free in S.C. (Miocene)
 Hominids develop and the Grand
Canyon forms (Pliocene)
Quaternary:
 Modern humans develop and ice
sheets are predominant- Ice age
(Pleistocene)
 Holocene Humans flourish
(Holocene)
PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002
34
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35. Summarize how scientists study Earth’s past environment and diverse life-forms by examining different types of fossils
(including molds, casts, petrified fossils, preserved and carbonized remains of plants and animals and trace fossils)
The study of Fossils
 A fossil is the preserved remains of an organism that has died. Fossils tell scientists,
called paleontologists, about living things such as their biology and environmental
conditions over earth’s history through the rock record. In addition, they give clues to
the conditions of the earth (i.e. climate) at the time that the fossil was preserved and
possibly relate changes of an organism over time.
 Definitions of fossil types:
Mold fossils: when sediments bury an organism and the sediment hardens into rock. The
organism decays slowly inside the rock, leaving an cavity in the shape of the organism.
 Cast fossil: The cavity or mold mentioned above can filled in with mud. When the mud
hardens, it takes on the shape of the organism.
 Petrified fossil or permineralized fossil: Minerals like calcium can soak into the buried
remains of an organism. The mineral replaces the remaining bone and changes it into rock.
 Carbonized fossil: When organism parts are pressed between layers of mud or clay that
hardens over time, squeezing the decaying organism away and leaving a carbon imprint in
the rock, since all living things contain carbon.
 Trace fossil: When the mud or sand hardens into rock where a footprint, trail or burrow
was left behind.
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Standard 8-2.2

36.  The fossil record, like the rock record, is an important record for understanding life on
earth before the dawn of man.
 Extinctions and new life forms are also found within the fossil record.
 Fossils can also show structural similarities and differences in organisms over time
revealing the diversity of life forms on earth. Nearly 90 percent of organisms that have
lived on the earth are now extinct.
Carbon imprint of fish
remains, age unknown
Belemnite fossil (cast), cut
and polished. Related to
present-day squid. Extinct.
Brachiopods in a sandstone matrix and an
individual brachiopod cast. Extinct.
A trilobite cast from the
Mississippian Period. Extinct.
Ammonite fossil
(cast), cut and
polished. Related
to present-day
snail. Extinct.
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